Propulsion system for an aircraft

ABSTRACT

A hybrid-electric propulsion system includes a propulsor, a turbomachine, and an electrical system, the electrical system including an electric machine coupled to the turbomachine. A method for operating the propulsion system includes operating, by one or more computing devices, the turbomachine in a steady-state flight operating condition, the turbomachine rotating the propulsor when operated in the steady-state flight operating condition; receiving, by the one or more computing devices, a command to accelerate the turbomachine while operating the turbomachine in the steady-state flight operating condition; and providing, by the one or more computing devices, electrical power to the electric machine to add power to the turbomachine, the propulsor, or both in response to the received command to accelerate the turbomachine.

FIELD

The present subject matter relates generally to a hybrid-electricpropulsion system, and a method for increasing an acceleration of aturbomachine of the hybrid electric propulsion system from a steadystate operating condition during flight.

BACKGROUND

A conventional commercial aircraft generally includes a fuselage, a pairof wings, and a propulsion system that provides thrust. The propulsionsystem typically includes at least two aircraft engines, such asturbofan jet engines. Each turbofan jet engine is typically mounted to arespective one of the wings of the aircraft, such as in a suspendedposition beneath the wing, separated from the wing and fuselage.

When operating in a steady state operating condition during flight,active clearance control systems of the turbofan jet engines may closedown, or tighten up, clearances within, e.g., respective turbinesections of the turbofan jet engines. As will be appreciate, tighteningup the clearances may increase an efficiency of the turbofan jetengines. However, these clearances are not kept as close as wouldotherwise be desired in order to enable the turbofan jet engines torelatively quickly increase an effective power output if desired. Morespecifically, these clearances are not kept as close as would otherwisebe desired in order to allow the components within the turbofan jetengines to expand radially outwardly if need in response to a command toaccelerate the turbofan jet engines (the expansion resulting from, e.g.,an increased rotational speed, and/or an increased temperature to whichthe components are exposed).

Accordingly, a propulsion system for an aircraft capable of operatingturbomachines in an efficient manner with relatively low clearancesduring steady state flight operations, without sacrificing anacceleration response, would be useful.

BRIEF DESCRIPTION

Aspects and advantages of the invention will be set forth in part in thefollowing description, or may be obvious from the description, or may belearned through practice of the invention.

In an exemplary aspect of the present disclosure, a method is providedfor operating a turbomachine of a hybrid-electric propulsion system ofan aircraft. The hybrid-electric propulsion system includes a propulsor,a turbomachine, and an electrical system, the electrical systemincluding an electric machine coupled to the turbomachine. The methodincludes operating, by one or more computing devices, the turbomachinein a steady-state flight operating condition, the turbomachine rotatingthe propulsor when operated in the steady-state flight operatingcondition; receiving, by the one or more computing devices, a command toaccelerate the turbomachine while operating the turbomachine in thesteady-state flight operating condition; and providing, by the one ormore computing devices, electrical power to the electric machine to addpower to the turbomachine, the propulsor, or both in response to thereceived command to accelerate the turbomachine.

In certain exemplary aspects the method further includes maintaining, bythe one or more computing devices, a fuel flow to a combustion sectionof the turbomachine substantially constant for an initial time period inresponse to the received command to accelerate the turbomachine. Forexample, in certain exemplary aspects maintaining, by the one or morecomputing devices, the fuel flow to the combustion section of theturbomachine substantially constant for the initial time period includesmaintaining a rotational speed of a high pressure system of theturbomachine substantially constant for the initial time period,maintaining a temperature within the turbomachine substantially constantfor the initial time period, or both.

In certain exemplary aspects the method further includes increasing, bythe one or more computing devices, one or more clearances within theturbomachine using an active clearance control system of theturbomachine in response to the received command to accelerate theturbomachine.

For example, in certain exemplary aspects the method further includesmaintaining, by the one or more computing devices, a fuel flow to acombustion section of the turbomachine substantially constant for aninitial time period in response to the received command to acceleratethe turbomachine, and wherein increasing, by the one or more computingdevices, the one or more clearances within the turbomachine using theactive clearance control system includes increasing, by the one or morecomputing devices, the one or more clearances within the turbomachineusing the active clearance control system substantially simultaneouslywith maintaining, by the one or more computing devices, the fuel flow tothe combustion section of the turbomachine substantially constant for aninitial time period.

For example, in certain exemplary aspects increasing, by the one or morecomputing devices, the one or more clearances within the turbomachineusing the active clearance control system includes increasing, by theone or more computing devices, the one or more clearances within theturbomachine using the active clearance control system substantiallysimultaneously with providing, by the one or more computing devices,electrical power to the electric machine.

In certain exemplary aspects receiving, by the one or more computingdevices, the command to accelerate the turbomachine while operating theturbomachine in the steady-state operating condition includes receiving,by the one or more computing devices, a command to perform a stepclimate maneuver.

In certain exemplary aspects the hybrid electric propulsion systemfurther includes an electric energy storage unit, and wherein providing,by the one or more computing devices, electrical power to the electricmachine includes providing, by the one or more computing devices,electrical power to the electric machine from the electric energystorage unit.

For example, in certain exemplary aspects providing, by the one or morecomputing devices, electrical power to the electric machine from theelectric energy storage unit includes providing, by the one or morecomputing devices, at least about fifteen horsepower of mechanical powerto the turbomachine, the propulsor, or both with the electric machine.

In certain exemplary aspects operating, by one or more computingdevices, the turbomachine in the steady-state flight operating conditionincludes extracting, by the one or more computing devices, electricalpower from the electric machine. For example, in certain exemplaryaspects the hybrid electric propulsion system further includes anelectric energy storage unit, and wherein extracting, by the one or morecomputing devices, electrical power from the electric machine includesextracting, by the one or more computing devices, electrical power fromthe electric machine to the electric energy storage unit.

For example, in certain exemplary aspects the hybrid electric propulsionsystem further includes an electric energy storage unit, and wherein theelectric machine is a first electric machine, wherein the propulsor is afirst propulsor, wherein the hybrid electric propulsion system furtherincludes a second propulsor, wherein the electrical system furtherincludes a second electric machine coupled to the second propulsor, andwherein extracting, by the one or more computing devices, electricalpower from the electric machine includes extracting, by the one or morecomputing devices, electrical power from the first electric machine tothe electric energy storage unit, the second electric machine, or both.

In certain exemplary aspects the method further includes receiving, bythe one or more computing devices, data indicative of an operationalparameter of the turbomachine, and wherein providing, by the one or morecomputing devices, electrical power to the electric machine includesmodulating, by the one or more computing devices, an amount ofelectrical power provided to the electric machine based at least in parton the received data indicative of the operational parameter of theturbomachine. For example, in certain exemplary aspects the operationalparameter of the turbomachine is at least one of: a rotational speedparameter of one or more components of the turbomachine, a fuel flow toa combustion section of the turbomachine, an internal pressure of theturbomachine, or an internal temperature of the turbomachine.

In certain exemplary aspects the method further includes receiving, bythe one or more computing devices, data indicative of an operationalparameter of the turbomachine; and terminating, by the one or morecomputing devices, the provision of electrical power to the electricmachine based at least in part on the received data indicative of theoperational parameter of the turbomachine.

In certain exemplary aspects the hybrid electric propulsion systemfurther includes an electric energy storage unit, and the method furtherincludes receiving, by the one or more computing devices, dataindicative of a state of charge of the electric energy storage unit, andwherein providing, by the one or more computing devices, electricalpower to the electric machine includes modulating, by the one or morecomputing devices, an amount of electrical power provided to theelectric machine based at least in part on the received data indicativeof the state of charge of the electric energy storage unit.

In certain exemplary aspects the hybrid electric propulsion systemfurther includes an electric energy storage unit, and wherein the methodfurther includes receiving, by the one or more computing devices, dataindicative of a state of charge of the electric energy storage unit; andterminating, by the one or more computing devices, the provision ofelectrical power to the electric machine based at least in part on thereceived data indicative of the state of charge of the electric energystorage unit.

In certain exemplary embodiments, a hybrid-electric propulsion systemfor an aircraft is provided. The hybrid-electric propulsion systemincludes a propulsor; a turbomachine coupled to the propulsor fordriving the propulsor and generating thrust; an electrical systemincludes an electric machine and an electric energy storage unitelectrically connectable to the electric machine, the electric machinecoupled to the turbomachine; and a controller. The controller isconfigured to receive a command to accelerate the turbomachine whileoperating the turbomachine in a steady-state flight operating conditionand provide electrical power to the electric machine to add power to theturbomachine, the propulsor, or both in response to the received commandto accelerate the turbomachine.

In certain exemplary embodiments the turbomachine further includes acombustion section, and wherein the controller is further configured tomaintain a fuel flow to the combustion section of the turbomachinesubstantially constant for an initial time period in response to thereceived command to accelerate the turbomachine.

In certain exemplary embodiments the turbomachine further includes anactive clearance control system, and wherein the controller is furtherconfigured to increase one or more clearances within the turbomachineusing the active clearance control system of the turbomachine inresponse to the received command to accelerate the turbomachine.

These and other features, aspects and advantages of the presentinvention will become better understood with reference to the followingdescription and appended claims. The accompanying drawings, which areincorporated in and constitute a part of this specification, illustrateembodiments of the invention and, together with the description, serveto explain the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including thebest mode thereof, directed to one of ordinary skill in the art, is setforth in the specification, which makes reference to the appendedfigures, in which:

FIG. 1 is a top view of an aircraft according to various exemplaryembodiments of the present disclosure.

FIG. 2 is a schematic, cross-sectional view of a gas turbine enginemounted to the exemplary aircraft of FIG. 1.

FIG. 3 is a close-up view of an active clearance control system inaccordance with one exemplary embodiment of the present disclosure.

FIG. 4 is a schematic, cross-sectional view of an electric fan assemblyin accordance with an exemplary embodiment of the present disclosure.

FIG. 5 is a top view of an aircraft including a propulsion system inaccordance with another exemplary embodiment of the present disclosure.

FIG. 6 is a flow diagram of a method for operating a hybrid electricpropulsion system of an aircraft in accordance with an exemplary aspectof the present disclosure.

FIG. 7 is a flow diagram of an exemplary aspect of the exemplary methodfor operating a hybrid electric propulsion system of an aircraft of FIG.6.

FIG. 8 is a flow diagram of another exemplary aspect of the exemplarymethod for operating a hybrid electric propulsion system of an aircraftof FIG. 6.

FIG. 9 is a computing system according to example aspects of the presentdisclosure.

DETAILED DESCRIPTION

Reference will now be made in detail to present embodiments of theinvention, one or more examples of which are illustrated in theaccompanying drawings. The detailed description uses numerical andletter designations to refer to features in the drawings. Like orsimilar designations in the drawings and description have been used torefer to like or similar parts of the invention.

As used herein, the terms “first”, “second”, and “third” may be usedinterchangeably to distinguish one component from another and are notintended to signify location or importance of the individual components.

The terms “forward” and “aft” refer to relative positions within a gasturbine engine or vehicle, and refer to the normal operational attitudeof the gas turbine engine or vehicle. For example, with regard to a gasturbine engine, forward refers to a position closer to an engine inletand aft refers to a position closer to an engine nozzle or exhaust.

The terms “upstream” and “downstream” refer to the relative directionwith respect to a flow in a pathway. For example, with respect to afluid flow, “upstream” refers to the direction from which the fluidflows, and “downstream” refers to the direction to which the fluidflows. However, the terms “upstream” and “downstream” as used herein mayalso refer to a flow of electricity.

The singular forms “a”, “an”, and “the” include plural references unlessthe context clearly dictates otherwise.

Approximating language, as used herein throughout the specification andclaims, is applied to modify any quantitative representation that couldpermissibly vary without resulting in a change in the basic function towhich it is related. Accordingly, a value modified by a term or terms,such as “about”, “approximately”, and “substantially”, are not to belimited to the precise value specified. In at least some instances, theapproximating language may correspond to the precision of an instrumentfor measuring the value, or the precision of the methods or machines forconstructing or manufacturing the components and/or systems. Forexample, the approximating language may refer to being within a tenpercent margin.

Here and throughout the specification and claims, range limitations arecombined and interchanged, such ranges are identified and include allthe sub-ranges contained therein unless context or language indicatesotherwise. For example, all ranges disclosed herein are inclusive of theendpoints, and the endpoints are independently combinable with eachother.

The present disclosure is generally related to a hybrid electricpropulsion system having a turbomachine, a propulsor coupled to theturbomachine, and an electrical system. The electrical system includesan electric machine and an electric energy storage unit electricallyconnectable to the electric machine. Additionally, the electric machineis coupled to the turbomachine such that rotation of the turbomachinerotates the electric machine, and similarly, rotation of the electricmachine may rotate one or more components of the turbomachine.

Notably, in certain exemplary embodiments, the propulsor may be a firstpropulsor, the electric machine may be a first electric machine, thehybrid electric propulsion system may further include a secondpropulsor, and the electrical system may further include a secondelectric machine coupled to the second propulsor. In such a manner, thesecond electric machine may drive the second propulsor during at leastcertain operations to provide a propulsive benefit for the aircraft. Forexample, in certain exemplary embodiments, the turbomachine and firstpropulsor may be together configured as part of a turbofan engine andthe second propulsor may be configured as part of an electric propulsorassembly (e.g., an electric fan). Alternatively, in other exemplaryembodiments, the turbomachine and first propulsor may be togetherconfigured as part of a first turbofan engine and the second propulsormay be configured as part of a second turbofan engine (e.g., with asecond turbomachine coupled to the second electric machine and/or thesecond propulsor). Further, in other exemplary embodiments thesecomponents may be configured as part of, e.g., turboprop engines, or anyother suitable gas turbine engine.

In certain operations of the hybrid electric propulsion system, thehybrid electric propulsion system is operable to provide for arelatively high level of acceleration for the turbomachine, while alsoallowing the turbomachine to operate more efficiently duringsteady-state flight operations. For example, in certain exemplaryaspects, the hybrid electric propulsion system may receive a command toaccelerate the turbomachine while operating the turbomachine in asteady-state flight operating condition. The steady-state flightoperating condition may be, e.g., a cruise operating condition. Thehybrid electric propulsion system may provide electrical power to thefirst electric machine to add power to the turbomachine in response tothe received command to accelerate the turbomachine. The additionalpower added to the turbomachine may increase an acceleration of theturbomachine substantially instantaneously, providing a desirable,relatively quick acceleration response.

Notably, such may be particularly useful when, e.g., the turbomachineincludes an active clearance control system. For example, with such anexemplary aspect, the hybrid electric propulsion system may maintain arotational speed of a core of the turbomachine (i.e., of a high pressuresystem of the turbomachine) at a substantially constant rotational speedand temperature in response to receiving the command to accelerate theturbomachine, allowing the hybrid electric propulsion system to relax orloosen up the active clearance control system (i.e., increase clearanceswithin the turbomachine, such as radial clearances between variousturbine rotor blades and an outer flowpath liner) prior to acceleratingthe core of the turbomachine. During the time that the active clearancecontrol system is loosening up, the electric power provided to the firstelectric machine may provide the desired, relatively quick accelerationresponse of the turbomachine for the aircraft. Notably, as will bediscussed in greater detail below, in certain exemplary embodiments, theelectric machine may be coupled to a low pressure system of theturbomachine, such that adding power to the turbomachine through theelectric machine does not substantially affect a rotational speed of thehigh pressure system of the turbomachine.

In such a manner, the active clearance control system may be maintainedat a relatively tight clearance during the steady-state flightoperations, without worrying about acceleration response times, whichmay, in turn, allow for the turbomachine to be operated more efficientlyduring such steady-state flight operating conditions.

Referring now to the drawings, wherein identical numerals indicate thesame elements throughout the figures, FIG. 1 provides a top view of anexemplary aircraft 10 as may incorporate various embodiments of thepresent disclosure. As shown in FIG. 1, the aircraft 10 defines alongitudinal centerline 14 that extends therethrough, a lateraldirection L, a forward end 16, and an aft end 18. Moreover, the aircraft10 includes a fuselage 12, extending longitudinally from the forward end16 of the aircraft 10 to the aft end 18 of the aircraft 10, and anempennage 19 at the aft end of the aircraft 10. Additionally, theaircraft 10 includes a wing assembly including a first, port side wing20 and a second, starboard side wing 22. The first and second wings 20,22 each extend laterally outward with respect to the longitudinalcenterline 14. The first wing 20 and a portion of the fuselage 12together define a first side 24 of the aircraft 10, and the second wing22 and another portion of the fuselage 12 together define a second side26 of the aircraft 10. For the embodiment depicted, the first side 24 ofthe aircraft 10 is configured as the port side of the aircraft 10, andthe second side 26 of the aircraft 10 is configured as the starboardside of the aircraft 10.

Each of the wings 20, 22 for the exemplary embodiment depicted includesone or more leading edge flaps 28 and one or more trailing edge flaps30. The aircraft 10 further includes, or rather, the empennage 19 of theaircraft 10 includes, a vertical stabilizer 32 having a rudder flap (notshown) for yaw control, and a pair of horizontal stabilizers 34, eachhaving an elevator flap 36 for pitch control. The fuselage 12additionally includes an outer surface or skin 38. It should beappreciated however, that in other exemplary embodiments of the presentdisclosure, the aircraft 10 may additionally or alternatively includeany other suitable configuration. For example, in other embodiments, theaircraft 10 may include any other configuration of stabilizer.

Referring now also to FIGS. 2 and 4, the exemplary aircraft 10 of FIG. 1additionally includes a hybrid-electric propulsion system 50 having afirst propulsor assembly 52 and a second propulsor assembly 54. FIG. 2provides a schematic, cross-sectional view of the first propulsorassembly 52, and FIG. 4 provides a schematic, cross-sectional view ofthe second propulsor assembly 54. For the embodiment depicted, the firstpropulsor assembly 52 and second propulsor assembly 54 are eachconfigured in an underwing-mounted configuration. However, as will bediscussed below, one or both of the first and second propulsorassemblies 52, 54 may in other exemplary embodiments be mounted at anyother suitable location.

More particularly, referring generally to FIGS. 1 through 4, theexemplary hybrid-electric propulsion system 50 generally includes thefirst propulsor assembly 52 having a turbomachine and a prime propulsor(which, for the embodiment of FIG. 2 are configured together as a gasturbine engine, or rather as a turbofan engine 100), an electric machine56 (which for the embodiment depicted in FIG. 2 is an electricmotor/generator) drivingly coupled to the turbomachine, the secondpropulsor assembly 54 (which for the embodiment of FIG. 3 is configuredas an electric propulsor assembly 200), an electric energy storage unit55 (electrically connectable to the electric machine 56 and/or theelectric propulsor assembly 200, a controller 72, and a power bus 58.The electric propulsor assembly 200, the electric energy storage unit55, and the electric machine 56 are each electrically connectable to oneanother through one or more electric lines 60 of the power bus 58. Forexample, the power bus 58 may include various switches or other powerelectronics movable to selectively electrically connect the variouscomponents of the hybrid electric propulsion system 50. Additionally,the power bus 58 may further include power electronics, such asinverters, converters, rectifiers, etc., for conditioning or convertingelectrical power within the hybrid electric propulsion system 50.

As will be appreciated, the controller 72 may be configured todistribute electrical power between the various components of thehybrid-electric propulsion system 50. For example, the controller 72 maybe operable with the power bus 58 (including the one or more switches orother power electronics) to provide electrical power to, or drawelectrical power from, the various components, such as the electricmachine 56, to operate the hybrid electric propulsion system 50 betweenvarious operating modes and perform various functions. Such is depictedschematically as the electric lines 60 of the power bus 58 extendingthrough the controller 72, and will be discussed in greater detailbelow.

The controller 72 may be a stand-alone controller, dedicated to thehybrid-electric propulsion system 50, or alternatively, may beincorporated into one or more of a main system controller for theaircraft 10, a separate controller for the exemplary turbofan engine 100(such as a full authority digital engine control system for the turbofanengine 100, also referred to as a FADEC), etc. For example, thecontroller 72 may be configured in substantially the same manner as theexemplary computing system 500 described below with reference to FIG. 6(and may be configured to perform one or more of the functions of theexemplary method 300, described below).

Additionally, the electric energy storage unit 55 may be configured asone or more batteries, such as one or more lithium-ion batteries, oralternatively may be configured as any other suitable electrical energystorage devices. It will be appreciated that for the hybrid-electricpropulsion system 50 described herein, the electric energy storage unit55 is configured to store a relatively large amount of electrical power.For example, in certain exemplary embodiments, the electric energystorage unit may be configured to store at least about fifty kilowatthours of electrical power, such as at least about sixty-five kilowatthours of electrical power, such as at least about seventy-five kilowattshours of electrical power, and up to about one thousand kilowatt hoursof electrical power.

Referring now particularly to FIGS. 1 and 2, the first propulsorassembly 52 includes a gas turbine engine mounted, or configured to bemounted, to the first wing 20 of the aircraft 10. More specifically, forthe embodiment of FIG. 2, the gas turbine engine includes a turbomachine102 and a propulsor, the propulsor being a fan (referred to as “fan 104”with reference to FIG. 2). Accordingly, for the embodiment of FIG. 2,the gas turbine engine is configured as a turbofan engine 100.

The turbofan engine 100 defines an axial direction A1 (extendingparallel to a longitudinal centerline 101 provided for reference) and aradial direction R1. As stated, the turbofan engine 100 includes the fan104 and the turbomachine 102 disposed downstream from the fan 104.

The exemplary turbomachine 102 depicted generally includes asubstantially tubular outer casing 106 that defines an annular inlet108. The outer casing 106 encases, in serial flow relationship, acompressor section including a booster or low pressure (LP) compressor110 and a high pressure (HP) compressor 112; a combustion section 114; aturbine section including a first, high pressure (HP) turbine 116 and asecond, low pressure (LP) turbine 118; and a jet exhaust nozzle section120. The compressor section, combustion section 114, and turbine sectiontogether define at least in part a core air flowpath 121 through theturbomachine 102.

The exemplary turbomachine 102 of the turbofan engine 100 additionallyincludes one or more shafts rotatable with at least a portion of theturbine section and, for the embodiment depicted, at least a portion ofthe compressor section. More particularly, for the embodiment depicted,the turbofan engine 100 includes a high pressure (HP) shaft or spool122, which drivingly connects the HP turbine 116 to the HP compressor112. Additionally, the exemplary turbofan engine 100 includes a lowpressure (LP) shaft or spool 124, which drivingly connects the LPturbine 118 to the LP compressor 110.

Additionally, it will be appreciated that the exemplary turbomachine 102depicted in FIG. 2 further includes an active clearance control system160. Specifically, referring now also briefly to FIG. 3, providing aclose-up view of the exemplary active clearance control system 160, forthe embodiment depicted, the active clearance control system 160 ispositioned within the turbine section of the turbomachine 102, and morespecifically is operable with the HP turbine 116 of the turbomachine102. For the embodiment depicted, the active clearance control system160 generally includes an actuating member 162 movable generally alongthe radial direction R1.

As will be appreciated, the active clearance control system 160 isgenerally configured to maintain desired clearances within the turbinesection despite, e.g., thermal expansion of one or more componentstherein. Specifically, as is depicted, the HP turbine 116 generallyincludes a plurality of HP turbine rotor blades 164. The HP turbinerotor blades 164 define a radially outer tip that defines a clearance166 with an outer liner 168, the outer liner 168 defining at least inpart the core air flowpath 121. By moving the actuating member 162 alongthe radial direction R1, the active clearance control system 160 maymove the liner 168 surrounding the plurality of HP turbine rotor blades164 radially inward or radially outward to increase or decrease theclearance 166. For example, it may generally be desirable to increasethe clearance 166 during an acceleration of the turbomachine 102 toallow the plurality of HP turbine rotor blades 164 to expand along theradial direction R1 due to the increased rotational speed and/orincreased temperature to which they are exposed. By contrast, maygenerally be desirable to decrease the clearance 166 during operation ofthe turbomachine 102 at steady-state flight operating conditions toincrease an efficiency of the turbomachine 102. Although depicted beingoperable with the HP turbine 116, in other exemplary embodiments, theactive clearance control system 160 may further be operable with, e.g.,the LP turbine 118. Additionally, in other exemplary embodiments of thepresent disclosure, the active clearance control system 160 may have anyother suitable configuration.

Referring back specifically to FIG. 2, the exemplary fan 104 depicted isconfigured as a variable pitch fan having a plurality of fan blades 128coupled to a disk 130 in a spaced apart manner. The fan blades 128extend outwardly from disk 130 generally along the radial direction R1.Each fan blade 128 is rotatable relative to the disk 130 about arespective pitch axis P1 by virtue of the fan blades 128 beingoperatively coupled to a suitable actuation member 132 configured tocollectively vary the pitch of the fan blades 128. The fan 104 ismechanically coupled to the LP shaft 124, such that the fan 104 ismechanically driven by the second, LP turbine 118. More particularly,the fan 104, including the fan blades 128, disk 130, and actuationmember 132, is mechanically coupled to the LP shaft 124 through a powergearbox 134, and is rotatable about the longitudinal axis 101 by the LPshaft 124 across the power gear box 134. The power gear box 134 includesa plurality of gears for stepping down the rotational speed of the LPshaft 124 to a more efficient rotational fan speed. Accordingly, the fan104 is powered by an LP system (including the LP turbine 118) of theturbomachine 102.

Referring still to the exemplary embodiment of FIG. 2, the disk 130 iscovered by rotatable front hub 136 aerodynamically contoured to promotean airflow through the plurality of fan blades 128. Additionally, theturbofan engine 100 includes an annular fan casing or outer nacelle 138that circumferentially surrounds the fan 104 and/or at least a portionof the turbomachine 102. Accordingly, the exemplary turbofan engine 100depicted may be referred to as a “ducted” turbofan engine. Moreover, thenacelle 138 is supported relative to the turbomachine 102 by a pluralityof circumferentially-spaced outlet guide vanes 140. A downstream section142 of the nacelle 138 extends over an outer portion of the turbomachine102 so as to define a bypass airflow passage 144 therebetween.

Referring still to FIG. 2, the hybrid-electric propulsion system 50additionally includes an electric machine 56, which for the embodimentdepicted is configured as an electric motor/generator. The electricmachine 56 is, for the embodiment depicted, positioned within theturbomachine 102 of the turbofan engine 100, inward of the core airflowpath 121, and is coupled to/in mechanical communication with one ofthe shafts of the turbofan engine 100. More specifically, for theembodiment depicted, the electric machine is coupled to the second, LPturbine 118 through the LP shaft 124. The electric machine 56 may beconfigured to convert mechanical power of the LP shaft 124 to electricalpower (such that the LP shaft 124 drives the electric machine 56), oralternatively the electric machine 56 may be configured to convertelectrical power provided thereto into mechanical power for the LP shaft124 (such that the electric machine 56 drives, or assists with driving,the LP shaft 124).

It should be appreciated, however, that in other exemplary embodiments,the electric machine 56 may instead be positioned at any other suitablelocation within the turbomachine 102 or elsewhere. For example, theelectric machine 56 may be, in other embodiments, mounted coaxially withthe LP shaft 124 within the turbine section, or alternatively may beoffset from the LP shaft 124 and driven through a suitable gear train.Additionally, or alternatively, in other exemplary embodiments, theelectric machine 56 may instead be powered by the HP system, i.e., bythe HP turbine 116 through, e.g., the HP shaft 122, or by both the LPsystem (e.g., the LP shaft 124) and the HP system (e.g., the HP shaft122) via a dual drive system. Additionally, or alternatively, still, inother embodiments, the electric machine 56 may include a plurality ofelectric machines, e.g., with one being drivingly connected to the LPsystem (e.g., the LP shaft 124) and one being drivingly connected to theHP system (e.g., the HP shaft 122). Further, although the electricmachine 56 is described as an electric motor/generator, in otherexemplary embodiments, the electric machine 56 may be configured solelyas an electric generator.

Notably, in certain exemplary embodiments, the electric machine 56 maybe configured to generate at least about ten kilowatts of electricalpower when driven by the turbomachine 102, such as at least about fiftykilowatts of electrical power, such as at least about sixty-fivekilowatts of electrical power, such as at least about seventy-fivekilowatts of electrical power, such as at least about one hundredkilowatts of electrical power, such as up to five thousand kilowatts ofelectrical power. Additionally, or alternatively, the electric machine56 may be configured to provide, or otherwise add, at least aboutfifteen horsepower of mechanical power to the turbomachine 102 when theelectric machine 56 is provided electrical power from, e.g., theelectric energy storage unit 55. For example, in certain exemplaryembodiments, the electric machine 56 may be configured to provide atleast about fifty horsepower mechanical power to the turbomachine 102,such as at least about seventy-five horsepower, such as at least aboutone hundred horsepower, such as at least about one hundred and twentyhorsepower, such as up to about seven thousand horsepower.

Referring still to FIGS. 1 and 2, the turbofan engine 100 furtherincludes a controller 150 and a plurality of sensors (not shown). Thecontroller 150 may be a full authority digital engine control system,also referred to as a FADEC. The controller 150 of the turbofan engine100 may be configured to control operation of, e.g., the actuationmember 132, the fuel delivery system, etc. Additionally, referring backalso to FIG. 1, the controller 150 of the turbofan engine 100 isoperably connected to the controller 72 of the hybrid-electricpropulsion system 50. Moreover, as will be appreciated, the controller72 may further be operably connected to one or more of the firstpropulsor assembly 52 (including controller 150), the electric machine56, the second propulsor assembly 54, and the energy storage unit 55through a suitable wired or wireless communication system (depicted inphantom).

Moreover, although not depicted, in certain exemplary embodiments, theturbofan engine 100 may further include one or more sensors positionedto, and configured to, sense data indicative of one or more operationalparameters of the turbofan engine 100. For example, the turbofan engine100 may include one or more temperature sensors configured to sense atemperature within a core air flowpath 121 of the turbomachine 102.Additionally, or alternatively, the turbofan engine 100 may include oneor more sensors configured to sense an exhaust gas temperature at anexit of the combustion section 114. Additionally, or alternatively,still, the turbofan engine 100 may include one or more pressure sensorsconfigured to sense data indicative of a pressure within the core airflowpath 121 of the turbomachine 102, such as within a combustor withinthe combustion section 114 of the turbomachine 102. Further, in stillother exemplary embodiments, the turbofan engine 100 one or more speedsensors configured to sense data indicative of a rotational speed of oneor more components of the turbofan engine 100, such as one or more ofthe LP spool 124 or HP spool 122.

It should further be appreciated that the exemplary turbofan engine 100depicted in FIG. 2 may, in other exemplary embodiments, have any othersuitable configuration. For example, in other exemplary embodiments, thefan 104 may not be a variable pitch fan, and further, in other exemplaryembodiments, the LP shaft 124 may be directly mechanically coupled tothe fan 104 (i.e., the turbofan engine 100 may not include the gearbox134). Further, it should be appreciated that in other exemplaryembodiments, the turbofan engine 100 may be configured as any othersuitable gas turbine engine. For example, in other embodiments, theturbofan engine 100 may instead be configured as a turboprop engine, anunducted turbofan engine, a turbojet engine, a turboshaft engine, etc.

Referring now particularly to FIGS. 1 and 4, as previously stated theexemplary hybrid-electric propulsion system 50 additionally includes thesecond propulsor assembly 54 mounted, for the embodiment depicted, tothe second wing 22 of the aircraft 10. Referring particularly to FIG. 4,the second propulsor assembly 54 is generally configured as an electricpropulsor assembly 200 including an electric motor 206 and apropulsor/fan 204. The electric propulsor assembly 200 defines an axialdirection A2 extending along a longitudinal centerline axis 202 thatextends therethrough for reference, as well as a radial direction R2.For the embodiment depicted, the fan 204 is rotatable about thecenterline axis 202 by the electric motor 206.

The fan 204 includes a plurality of fan blades 208 and a fan shaft 210.The plurality of fan blades 208 are attached to/rotatable with the fanshaft 210 and spaced generally along a circumferential direction of theelectric propulsor assembly 200 (not shown). In certain exemplaryembodiments, the plurality of fan blades 208 may be attached in a fixedmanner to the fan shaft 210, or alternatively, the plurality of fanblades 208 may be rotatable relative to the fan shaft 210, such as inthe embodiment depicted. For example, the plurality of fan blades 208each define a respective pitch axis P2, and for the embodiment depictedare attached to the fan shaft 210 such that a pitch of each of theplurality of fan blades 208 may be changed, e.g., in unison, by a pitchchange mechanism 211. Changing the pitch of the plurality of fan blades208 may increase an efficiency of the second propulsor assembly 54and/or may allow the second propulsor assembly 54 to achieve a desiredthrust profile. With such an exemplary embodiment, the fan 204 may bereferred to as a variable pitch fan.

Moreover, for the embodiment depicted, the electric propulsor assembly200 depicted additionally includes a fan casing or outer nacelle 212,attached to a core 214 of the electric propulsor assembly 200 throughone or more struts or outlet guide vanes 216. For the embodimentdepicted, the outer nacelle 212 substantially completely surrounds thefan 204, and particularly the plurality of fan blades 208. Accordingly,for the embodiment depicted, the electric propulsor assembly 200 may bereferred to as a ducted electric fan.

Referring still particularly to FIG. 4, the fan shaft 210 ismechanically coupled to the electric motor 206 within the core 214, suchthat the electric motor 206 drives the fan 204 through the fan shaft210. The fan shaft 210 is supported by one or more bearings 218, such asone or more roller bearings, ball bearings, or any other suitablebearings. Additionally, the electric motor 206 may be an inrunnerelectric motor (i.e., including a rotor positioned radially inward of astator), or alternatively may be an outrunner electric motor (i.e.,including a stator positioned radially inward of a rotor), oralternatively, still, may be an axial flux electric motor (i.e., withthe rotor neither outside the stator nor inside the stator, but ratheroffset from it along the axis of the electric motor).

As briefly noted above, the electrical power source (e.g., the electricmachine 56 or the electric energy storage unit 55) is electricallyconnected with the electric propulsor assembly 200 (i.e., the electricmotor 206) for providing electrical power to the electric propulsorassembly 200. More particularly, the electric motor 206 is in electricalcommunication with the electric machine 56 and/or the electric energystorage unit 55 through the electrical power bus 58, and moreparticularly through the one or more electrical cables or lines 60extending therebetween.

It should be appreciated, however, that in other exemplary embodimentsthe exemplary hybrid-electric propulsion system 50 may have any othersuitable configuration, and further, may be integrated into an aircraft10 in any other suitable manner. For example, in other exemplaryembodiments, the electric propulsor assembly 200 of the hybrid electricpropulsion system 50 may instead be configured as a plurality ofelectric propulsor assemblies 200 and/or the hybrid electric propulsionsystem 50 may further include a plurality of gas turbine engines (suchas turbofan engine 100) and electric machines 56.

Further, in other exemplary embodiments, the electric propulsorassembly(ies) 200 and/or gas turbine engine(s) and electric machine(s)56 may be mounted to the aircraft 10 at any other suitable location inany other suitable manner (including, e.g., tail mountedconfigurations). For example, in certain exemplary embodiments, theelectric propulsor assembly may be configured to ingest boundary layerair and reenergize such boundary layer air to provide a propulsivebenefit for the aircraft (the propulsive benefit may be thrust, or maysimply be an increase in overall net thrust for the aircraft by reducinga drag on the aircraft).

Moreover, in still other exemplary embodiments, the exemplary hybridelectric propulsion system 50 may have still other configurations. Forexample, in other exemplary embodiments, the hybrid electric propulsionsystem 50 may not include a “pure” electric propulsor assembly. Forexample, referring now briefly to FIG. 5, a schematic diagram of ahybrid-electric propulsion system 50 in accordance with yet anotherexemplary embodiment of the present disclosure is provided. Theexemplary hybrid electric propulsion system 50 depicted in FIG. 5 may beconfigured in a similar manner as one or more the exemplary hybridelectric propulsion systems 50 described above with reference to FIGS. 1through 4.

For example, the exemplary hybrid-electric propulsion system 50 of FIG.5 generally includes a first propulsor assembly 52 and a secondpropulsor assembly 54. The first propulsor assembly generally includes afirst turbomachine 102A and a first propulsor 104A, and similarly, thesecond propulsor assembly 54 generally includes a second turbomachine102B and a second propulsor 104B. Each of the first and secondturbomachines 102A, 102B generally includes a low pressure system havinga low pressure compressor 110 drivingly coupled to a low pressureturbine 118 through a low pressure shaft 124, as well as a high pressuresystem having a high pressure compressor 112 drivingly coupled to a highpressure turbine 116 through a high pressure shaft 122 (sometimes alsoreferred to as a “core” of the turbomachine). Additionally, the firstpropulsor 104A is drivingly coupled to the low pressure system of thefirst turbomachine 102A and the second propulsor 104B is drivinglycoupled to the low pressure system of the second turbomachine 102B. Incertain exemplary embodiments, the first propulsor 104A and firstturbomachine 102A may be configured as a first turbofan engine andsimilarly, the second propulsor 104B and second turbomachine 102B may beconfigured as a second turbofan engine (e.g., similar to the exemplaryturbofan engine 100 of FIG. 2). Alternatively, however, these componentsmay instead be configured as parts of a turboprop engine or any othersuitable turbomachine-driven propulsion device. Further, in certainexemplary embodiments, the first propulsor assembly 52 may be mounted toa first wing of an aircraft and the second propulsor assembly 54 may bemounted to a second wing of the aircraft (similar, e.g., to theexemplary embodiment of FIG. 1). Of course, in other exemplaryembodiments, any other suitable configuration may be provided (e.g.,both may be mounted to the same wing, one or both may be mounted to atail of the aircraft, etc.).

Moreover, the hybrid electric propulsion system 50 of FIG. 5additionally includes an electrical system. The electrical systemincludes a first electric machine 56A, a second electric machine 56B,and an electric energy storage unit 55 electrically connectable to thefirst electric machine 56A and the second electric machine 56B. Thefirst electric machine 56A is additionally coupled to the firstturbomachine 102A. More specifically, for the embodiment depicted, thefirst electric machine 56A is coupled to the high pressure system of thefirst turbomachine 102A, and more specifically still, is coupled to thehigh-pressure spool 122 of the first turbomachine 102A. In such amanner, the first electric machine 56A may extract power from the highpressure system of the first turbomachine 102A and/or provide power tothe high-pressure system of the first turbomachine 102A.

Further, it will be appreciated that for the embodiment depicted, thesecond propulsor assembly 54 is not configured as a pure electricpropulsor assembly. Instead, the second propulsor assembly 54 isconfigured as part of a hybrid electric propulsor. More particularly,the second electric machine 56B is coupled to the second propulsor 104B,and is further coupled to the low pressure system of the secondturbomachine 102B. In such a manner, the second electric machine 56B mayextract power from the low pressure system of the second turbomachine102B and/or provide power to the low pressure system of the firstturbomachine 102A. More particularly, in certain exemplary aspects, thesecond electric machine 56B may drive, or assist with driving the secondpropulsor 104B, such that the second electric machine 56B may providepower to the second turbomachine 102B, the second propulsor 104B, orboth.

As is also depicted in FIG. 5, the exemplary hybrid electric propulsionsystem 50 further includes a controller 72 and a power bus 58. The firstelectric machine 56A, the second electric machine 56B, and the electricenergy storage unit 55 are each electrically connectable to one anotherthrough one or more electric lines 60 of the power bus 58. For example,the power bus 58 may include various switches or other power electronicsmovable to selectively electrically connect the various components ofthe hybrid electric propulsion system 50, and optionally to convert orcondition such electrical power transferred therethrough.

Furthermore, it should be appreciated that in still other exemplaryembodiments, the exemplary hybrid electric propulsion system 50 may haveother suitable configurations. For example, although the exemplaryembodiment of FIG. 5 includes a first electric machine 56A coupled tothe high-pressure system of the first turbomachine 102A and the secondelectric machine 56B coupled to the low pressure system of the secondturbomachine 102B, in other exemplary embodiments, each of the electricmachines 56A, 56B may be coupled to the low pressure system, oralternatively may be coupled to the high-pressure system. Alternatively,in other exemplary embodiments the electrical system may further includean additional electric machine coupled to the low pressure system of thefirst turbomachine 102A and/or an additional electric machine coupled tothe high-pressure system of the second turbomachine 102B.

Referring now to FIG. 6, a flow diagram of a method 300 for operating ahybrid electric propulsion system of an aircraft is provided. The method300 may generally be operable with one or more of the exemplary hybridelectric propulsion systems described above with reference to FIGS. 1through 5. For example, the hybrid electric propulsion system maygenerally include a turbomachine, a propulsor coupled to theturbomachine, and an electrical system, with the electrical systemincluding an electric machine coupled to the turbomachine and anelectric energy storage unit. The electric energy storage unit may beelectrically connectable to the electric machine.

As is depicted, the method 300 includes at (302) operating, by the oneor more computing devices, the turbomachine in a steady-state flightoperating condition. For example, in at least certain exemplary aspects,operating, by the one or more computing devices, the turbomachine in thesteady-state flight operating condition at (302) includes operating, bythe one or more computing devices, the turbomachine in a cruiseoperating condition. Additionally, it will be appreciated that theturbomachine rotates the propulsor when operated in the steady-stateflight operating condition. More specifically, the turbomachine at leastin part rotates the propulsor when operated in the steady-state flightoperating condition. Accordingly, while in some exemplary aspects theturbomachine solely rotates the propulsor, in at least certain exemplaryaspects, the propulsor may further be rotated in part by the electricmachine, such that the turbomachine and electric machine together drivethe propulsor during such steady-state flight operating condition.

Notably, during such steady-state flight operating conditions, thehybrid electric propulsion system may generally be operable todistribute electrical power amongst its components. For example, for theexemplary aspect of the method 300 depicted in FIG. 6, operating, by theone or more computing devices, the turbomachine in the steady-stateflight operating condition at (302) further includes at (304)extracting, by the one or more computing devices, electrical power fromthe electric machine. More specifically, for the exemplary aspectdepicted, extracting, by the one or more computing devices, electricalpower from the electric machine at (304) includes at (306) extracting,by the one or more computing devices, electrical power from the electricmachine to the electric energy storage unit.

Further, as will be appreciated from the discussion above, in at leastcertain exemplary aspects the hybrid electric propulsion system mayfurther include a plurality of electric machines and/or propulsors. Forexample, in certain exemplary aspects, the electric machine may be afirst electric machine, the propulsor may be a first propulsor, thehybrid electric propulsion system may further include a secondpropulsor, and the electrical system may further include a secondelectric machine coupled to the second propulsor. With such an exemplaryaspect, extracting, by the one or more computing devices, electricalpower from the electric machine at (304) may further include, as isdepicted in phantom, at (308) extracting, by the one or more computingdevices, electrical power from the first electric machine to theelectric energy storage unit, the second electric machine, or both. Forexample, in certain exemplary aspects, extracting, by the one or morecomputing devices, electrical power from the electric machine at (308)may further include, extracting, by the one or more computing devices,electrical power from the first electric machine to the second electricmachine.

Referring still to the exemplary aspect of the method 300 depicted, themethod 300 further includes at (310) receiving, by the one or morecomputing devices, a command to accelerate the turbomachine whileoperating the turbomachine in the steady-state flight operatingcondition at (302). For example, in at least certain exemplary aspects,such as the exemplary aspect depicted, receiving, by the one or morecomputing devices, the command to accelerate the turbomachine whileoperating the turbomachine in the steady-state operating condition at(310) may include at (312) receiving, by the one or more computingdevices, a command to perform a step climb maneuver. As will beappreciated, the step climb maneuver refers generally to a maneuverduring flight operations to take an aircraft cruising a first altitudeto a second, higher altitude. An increased amount of thrust is generallyrequired to perform such maneuver, as compared to the amount of thrustrequired during the immediately preceding cruise operations.

Further, the exemplary aspect of the method 300 depicted furtherincludes at (314) providing, by the one or more computing devices,electrical power to the electric machine to add power to theturbomachine, the propulsor, or both in response to the received commandto accelerate turbomachine at (310). Notably, the provision ofelectrical power to the electric machine at (314) may, by adding suchpower to the turbomachine, the propulsor, or both, increase anacceleration of the turbomachine (or provide an increased thrustgenerated by the propulsor), providing a substantially instantaneouseffective power increase for the electric machine in response to thecommand to accelerate the turbomachine received at (310).

For the exemplary aspect depicted, providing, by the one or morecomputing devices, electrical power to the electric machine at (314)includes at (316) providing, by the one or more computing devices,electrical power to the electric machine from the electric energystorage unit. More specifically, for the exemplary aspect depicted,providing, by the one or more computing devices, electrical power to theelectric machine from the electric energy storage unit at (314) includesat (318) providing, by the one or more computing devices, at least aboutfifteen horsepower of mechanical power to the turbomachine, thepropulsor, or both with the electric machine (note that as used herein,the amount of power provided, if provided to “both” the turbomachine andthe propulsor is a sum of all power provided by the electric machine tothe turbomachine and propulsor). In such a manner, the method 300 maygenerally provide a desired acceleration increase in response to thecommand to accelerate the turbomachine while operating the turbomachinein the steady-state flight operating condition is received at (310).

Notably, in at least certain exemplary aspects, providing, the one ormore computing devices, electrical power to the electric machine to addpower to the turbomachine, the propulsor, or both in response to thereceived command to accelerate the turbomachine at (314) may includeproviding a substantially constant/consistent amount of electrical powerto the electric machine. However, referring now briefly to FIG. 7,providing a flow diagram of an exemplary aspect of the method 300 ofFIG. 6, in other exemplary aspects, such as the exemplary aspectdepicted, providing, by the one or more computing devices, electricalpower to the electric machine at (314) includes at (315) modulating, bythe one or more computing devices, an amount of electrical powerprovided to the electric machine. More specifically, the exemplaryaspect of the method 300 depicted in FIG. 7 further includes at (320)receiving, by the one or more computing devices, data indicative of anoperational parameter the turbomachine, and modulating, by the one ormore computing devices, the amount of electrical power provided to theelectric machine at (315) further includes at (321) modulating, by theone or more computing devices, an amount of electrical power provided tothe electric machine based at least in part on the received dataindicative of the operational parameter of the turbomachine. Forexample, in such a manner, the method 300 may reduce an amount ofelectrical power provided to the electric machine, as the electricmachine approaches a desired rotational speed, or a desired poweroutput.

In certain exemplary aspects, the operational parameter the turbomachinemay be a rotational speed parameter of one or more components of theturbomachine, such as a rotational speed, a rotational acceleration, ora combination thereof. Alternatively, the operational parameter of theturbomachine may be any other suitable operational parameter, such as atemperature within the turbomachine (such as an exhaust gastemperature), a pressure within the turbomachine, a fuel flow to acombustion section of the turbomachine, etc.

However, in other exemplary aspects, the method 300 may modulate anamount of electrical power provided to the electric machine at (315)based on any other suitable parameters. For example, in other exemplaryaspects, as is depicted in phantom in FIG. 7, the method 300 may furtherinclude at (322) receiving, by the one or more computing devices, dataindicative of a state of charge of the electric energy storage unit.Whit such an exemplary aspect, modulating, by the one or more computingdevices, the amount of electrical power provided to the electric machineat (315) may further include, as is depicted in phantom, at (323)modulating, by the one or more computing devices, an amount ofelectrical power provided to the electric machine based at least in parton the received data indicative of the state of charge of the electricenergy storage unit. For example, the method 300 may reduce an amount ofelectrical power provided to the electric machine when, for example, thecharge level of the electric energy storage unit falls below a certainthreshold, or approaches a certain threshold.

Referring back to FIG. 6, as stated, the method 300 may generally beoperable to provide a substantially immediate acceleration response oncethe command to accelerate the turbomachine while operating theturbomachine in the steady-state flight operating condition is receivedat (310). Accordingly, such may allow for the turbomachine to operatemore efficiently at the steady-state flight operating condition. Moreparticularly, for the exemplary aspect of FIG. 6, the turbomachinefurther includes an active clearance control system. The activeclearance control system may modify clearances between one or moreturbine rotor blades and an outer flowpath liner within a turbinesection of the turbomachine during operation of the turbomachine.Typically, when operating at a steady-state flight operation condition,the clearances are maintained larger than would otherwise be desirablefrom an efficiency standpoint in order to allow for a relatively quickacceleration of the turbomachine if desired. For example, as will beappreciated, an acceleration of the turbomachine from a steady-stateoperating condition increases a rotational speed of the turbine rotorblades, and also increases a temperature to which the turbine rotorblades and other components are exposed, resulting in an expansion ofthe turbine rotor blades and certain other components. The relativelylarge clearances are maintained to accommodate such expansion. However,given that the hybrid electric propulsion system of the presentdisclosure, and more specifically, the electric machine coupled to theturbomachine, may provide the substantially immediate accelerationresponse desired, the active clearance control system may be operated tomaintain relatively tight clearances between the turbine rotor bladesand, e.g., an outer flowpath liner within the turbine section. Forexample, for the exemplary aspect of the method 300 depicted, the activeclearance control system may maintain desired relatively tightclearances, and in response to receiving a command to accelerate theturbomachine (e.g., at (310)), provide the immediate power responsedesired through the electric machine, giving the active clearancecontrol system time to increase the clearances (i.e., “loosen-up”)enough to allow the turbomachine to accelerate through combustion.

Accordingly, for the exemplary aspect of the method 300 depicted, themethod 300 further includes at (324) increasing, by the one or morecomputing devices, one or more clearances within the turbomachine usingan active clearance control system in response to the received commandto accelerate the turbomachine at (310). The one or more clearances maybe turbine rotor blades clearances within, e.g., a high pressure turbine(and/or low pressure turbine) of the turbomachine. Specifically, for theembodiment exemplary aspect depicted, increasing, by the one or morecomputing devices, one or more clearances within the turbomachine usingthe active clearance control system at (324) includes at (326)increasing, by the one or more computing devices, one or more clearanceswithin the turbomachine using the active clearance control systemsubstantially simultaneously with providing, by the one or morecomputing devices, electrical power to the electric machine at (314).Furthermore, with such an exemplary aspect, increasing, by the one ormore computing devices, one or more clearances within the turbomachineusing the active clearance control system at (324) additionally includesat (328) maintaining, by the one or more computing devices, a fuel flowto a combustion section of the turbomachine substantially constant foran initial time period. Notably, as used herein, the term “substantiallyconstant” may refer to less than a five percent variance from an initialvalue. For example, in at least certain exemplary aspects, maintaining,by the one or more computing devices, a fuel flow to a combustionsection of the turbomachine substantially constant for the initial timeperiod at (328) may accordingly include maintaining a rotational speedof a high pressure system of the turbomachine substantially constant forthe initial time period and/or maintaining a temperature within aspecific section of the turbomachine (e.g., an exhaust gas temperature)substantially constant for the initial time period.

The initial time period may be an amount of time sufficient for theactive clearance control system to loosen up enough to allow the highpressure system of the turbomachine to accelerate. For example, incertain exemplary aspects, the initial time period may be at least abouttwo seconds, such as at least about five seconds, such as up to aboutten seconds, such as up to about five minutes.

Furthermore, referring now also briefly to FIG. 8, providing anotherflowchart of an exemplary aspect of the method 300, the method 300further includes at (330) terminating, by the one or more computingdevices, the provision electrical power provided to the electric machineat (314) to add power to the turbomachine, the propulsor, or both inresponse to received command to accelerate the turbomachine. Morespecifically, for the exemplary aspect depicted, terminating, by the oneor more computing devices, the provision of electrical power provided tothe electric machine at (330) includes at (332) terminating, by the oneor more computing devices, the provision of electrical power provided tothe electric machine at (314) based at least in part on the receiveddata indicative of the operational parameter of the turbomachine at(320). For example, the method 300 may determine the turbomachine isrotating at a desired speed, or operating a desired power level, andterminate the provision of electrical power to the electric machinebased on such a determination.

Alternatively, however, in other exemplary aspects, the method 300 mayterminate provision electrical power to the electric machine based onany other suitable determination. For example, in other exemplaryaspects, terminating, by the one or more computing devices, theprovision of electrical power provided to the electric machine at (330)may include, as is depicted in phantom, at (334) terminating, by the oneor more computing device, the provision electrical power provided to theelectric machine at (314) based at least in part on the received dataindicative of the state of charge the electric energy storage unit at(322). For example, the method 300 may determine a charge level of theelectric energy storage unit is below a predetermined threshold, orapproaching a predetermined threshold, and terminate the provisionelectrical power to the electric machine based on such a determination.

Operating the hybrid electric propulsion system in accordance with oneor more of the above exemplary aspects may provide for an overall moreefficient hybrid electric propulsion system, and more specifically for amore efficient turbomachine.

Referring now to FIG. 9, an example computing system 500 according toexample embodiments of the present disclosure is depicted. The computingsystem 500 can be used, for example, as a controller 72 in a hybridelectric propulsion system 50. The computing system 500 can include oneor more computing device(s) 510. The computing device(s) 510 can includeone or more processor(s) 510A and one or more memory device(s) 510B. Theone or more processor(s) 510A can include any suitable processingdevice, such as a microprocessor, microcontroller, integrated circuit,logic device, and/or other suitable processing device. The one or morememory device(s) 510B can include one or more computer-readable media,including, but not limited to, non-transitory computer-readable media,RAM, ROM, hard drives, flash drives, and/or other memory devices.

The one or more memory device(s) 510B can store information accessibleby the one or more processor(s) 510A, including computer-readableinstructions 510C that can be executed by the one or more processor(s)510A. The instructions 510C can be any set of instructions that whenexecuted by the one or more processor(s) 510A, cause the one or moreprocessor(s) 510A to perform operations. In some embodiments, theinstructions 510C can be executed by the one or more processor(s) 510Ato cause the one or more processor(s) 510A to perform operations, suchas any of the operations and functions for which the computing system500 and/or the computing device(s) 510 are configured, the operationsfor operating a turbomachine (e.g, method 300), as described herein,and/or any other operations or functions of the one or more computingdevice(s) 510. Accordingly, the method 300 may be computer-implementedmethods. The instructions 510C can be software written in any suitableprogramming language or can be implemented in hardware. Additionally,and/or alternatively, the instructions 510C can be executed in logicallyand/or virtually separate threads on processor(s) 510A. The memorydevice(s) 510B can further store data 510D that can be accessed by theprocessor(s) 510A. For example, the data 510D can include dataindicative of power flows, data indicative of power demands of variousloads in a hybrid electric propulsion system, data indicative ofoperational parameters of the hybrid electric propulsion system,including of a turbomachine of the hybrid electric propulsion system.

The computing device(s) 510 can also include a network interface 510Eused to communicate, for example, with the other components of system500 (e.g., via a network). The network interface 510E can include anysuitable components for interfacing with one or more network(s),including for example, transmitters, receivers, ports, controllers,antennas, and/or other suitable components. One or more external displaydevices (not depicted) can be configured to receive one or more commandsfrom the computing device(s) 510.

The technology discussed herein makes reference to computer-basedsystems and actions taken by and information sent to and fromcomputer-based systems. One of ordinary skill in the art will recognizethat the inherent flexibility of computer-based systems allows for agreat variety of possible configurations, combinations, and divisions oftasks and functionality between and among components. For instance,processes discussed herein can be implemented using a single computingdevice or multiple computing devices working in combination. Databases,memory, instructions, and applications can be implemented on a singlesystem or distributed across multiple systems. Distributed componentscan operate sequentially or in parallel.

Although specific features of various embodiments may be shown in somedrawings and not in others, this is for convenience only. In accordancewith the principles of the present disclosure, any feature of a drawingmay be referenced and/or claimed in combination with any feature of anyother drawing.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they include structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal languages of the claims.

What is claimed is:
 1. A method for operating a turbomachine of ahybrid-electric propulsion system of an aircraft, the hybrid-electricpropulsion system comprising a propulsor, a turbomachine, and anelectrical system, the electrical system comprising an electric machinecoupled to the turbomachine, the method comprising: operating, by one ormore computing devices, the turbomachine in a steady-state flightoperating condition, the turbomachine rotating the propulsor whenoperated in the steady-state flight operating condition; receiving, bythe one or more computing devices, a command to accelerate theturbomachine while operating the turbomachine in the steady-state flightoperating condition; and providing, by the one or more computingdevices, electrical power to the electric machine to add power to theturbomachine, the propulsor, or both in response to the received commandto accelerate the turbomachine.
 2. The method of claim 1, furthercomprising: maintaining, by the one or more computing devices, a fuelflow to a combustion section of the turbomachine substantially constantfor an initial time period in response to the received command toaccelerate the turbomachine.
 3. The method of claim 2, whereinmaintaining, by the one or more computing devices, the fuel flow to thecombustion section of the turbomachine substantially constant for theinitial time period comprises maintaining a rotational speed of a highpressure system of the turbomachine substantially constant for theinitial time period, maintaining a temperature within the turbomachinesubstantially constant for the initial time period, or both.
 4. Themethod of claim 1, further comprising: increasing, by the one or morecomputing devices, one or more clearances within the turbomachine usingan active clearance control system of the turbomachine in response tothe received command to accelerate the turbomachine.
 5. The method ofclaim 4, further comprising: maintaining, by the one or more computingdevices, a fuel flow to a combustion section of the turbomachinesubstantially constant for an initial time period in response to thereceived command to accelerate the turbomachine, and wherein increasing,by the one or more computing devices, the one or more clearances withinthe turbomachine using the active clearance control system comprisesincreasing, by the one or more computing devices, the one or moreclearances within the turbomachine using the active clearance controlsystem substantially simultaneously with maintaining, by the one or morecomputing devices, the fuel flow to the combustion section of theturbomachine substantially constant for an initial time period.
 6. Themethod of claim 4, wherein increasing, by the one or more computingdevices, the one or more clearances within the turbomachine using theactive clearance control system comprises increasing, by the one or morecomputing devices, the one or more clearances within the turbomachineusing the active clearance control system substantially simultaneouslywith providing, by the one or more computing devices, electrical powerto the electric machine.
 7. The method of claim 1, wherein receiving, bythe one or more computing devices, the command to accelerate theturbomachine while operating the turbomachine in the steady-stateoperating condition comprises receiving, by the one or more computingdevices, a command to perform a step climate maneuver.
 8. The method ofclaim 1, wherein the hybrid electric propulsion system further comprisesan electric energy storage unit, and wherein providing, by the one ormore computing devices, electrical power to the electric machinecomprises providing, by the one or more computing devices, electricalpower to the electric machine from the electric energy storage unit. 9.The method of claim 8, wherein providing, by the one or more computingdevices, electrical power to the electric machine from the electricenergy storage unit comprises providing, by the one or more computingdevices, at least about fifteen horsepower of mechanical power to theturbomachine, the propulsor, or both with the electric machine.
 10. Themethod of claim 1, wherein operating, by one or more computing devices,the turbomachine in the steady-state flight operating conditioncomprises extracting, by the one or more computing devices, electricalpower from the electric machine.
 11. The method of claim 10, wherein thehybrid electric propulsion system further comprises an electric energystorage unit, and wherein extracting, by the one or more computingdevices, electrical power from the electric machine comprisesextracting, by the one or more computing devices, electrical power fromthe electric machine to the electric energy storage unit.
 12. The methodof claim 10, wherein the hybrid electric propulsion system furthercomprises an electric energy storage unit, and wherein the electricmachine is a first electric machine, wherein the propulsor is a firstpropulsor, wherein the hybrid electric propulsion system furthercomprises a second propulsor, wherein the electrical system furthercomprises a second electric machine coupled to the second propulsor, andwherein extracting, by the one or more computing devices, electricalpower from the electric machine comprises extracting, by the one or morecomputing devices, electrical power from the first electric machine tothe electric energy storage unit, the second electric machine, or both.13. The method of claim 1, further comprising: receiving, by the one ormore computing devices, data indicative of an operational parameter ofthe turbomachine, and wherein providing, by the one or more computingdevices, electrical power to the electric machine comprises modulating,by the one or more computing devices, an amount of electrical powerprovided to the electric machine based at least in part on the receiveddata indicative of the operational parameter of the turbomachine. 14.The method of claim 13, wherein the operational parameter of theturbomachine is at least one of: a rotational speed parameter of one ormore components of the turbomachine, a fuel flow to a combustion sectionof the turbomachine, an internal pressure of the turbomachine, or aninternal temperature of the turbomachine.
 15. The method of claim 1,further comprising: receiving, by the one or more computing devices,data indicative of an operational parameter of the turbomachine; andterminating, by the one or more computing devices, the provision ofelectrical power to the electric machine based at least in part on thereceived data indicative of the operational parameter of theturbomachine.
 16. The method of claim 1, wherein the hybrid electricpropulsion system further comprises an electric energy storage unit, andwherein the method further comprises: receiving, by the one or morecomputing devices, data indicative of a state of charge of the electricenergy storage unit, and wherein providing, by the one or more computingdevices, electrical power to the electric machine comprises modulating,by the one or more computing devices, an amount of electrical powerprovided to the electric machine based at least in part on the receiveddata indicative of the state of charge of the electric energy storageunit.
 17. The method of claim 1, wherein the hybrid electric propulsionsystem further comprises an electric energy storage unit, and whereinthe method further comprises: receiving, by the one or more computingdevices, data indicative of a state of charge of the electric energystorage unit; and terminating, by the one or more computing devices, theprovision of electrical power to the electric machine based at least inpart on the received data indicative of the state of charge of theelectric energy storage unit.
 18. A hybrid-electric propulsion systemfor an aircraft comprising: a propulsor; a turbomachine coupled to thepropulsor for driving the propulsor and generating thrust; an electricalsystem comprising an electric machine and an electric energy storageunit electrically connectable to the electric machine, the electricmachine coupled to the turbomachine; and a controller configured toreceive a command to accelerate the turbomachine while operating theturbomachine in a steady-state flight operating condition and provideelectrical power to the electric machine to add power to theturbomachine, the propulsor, or both in response to the received commandto accelerate the turbomachine.
 19. The hybrid-electric propulsionsystem of claim 18, wherein the turbomachine further comprises acombustion section, and wherein the controller is further configured tomaintain a fuel flow to the combustion section of the turbomachinesubstantially constant for an initial time period in response to thereceived command to accelerate the turbomachine.
 20. The hybrid-electricpropulsion system of claim 18, wherein the turbomachine furthercomprises an active clearance control system, and wherein the controlleris further configured to increase one or more clearances within theturbomachine using the active clearance control system of theturbomachine in response to the received command to accelerate theturbomachine.